Hello, Not sure that there is a link but since WIN10 (painfull) upgrade to 1803 version

1/ first time in P3D V4 : GSX was inactive, tried to activate via addon menu manager in P3D (reactivate the key), with no effect2/ I tried to install GSX again, and addon menu manager in P3D disappeared

I updated to Windows 10 1803 a week ago, no problems whatsoever with GSX.

If you are missing the Addon Manager or the GSX menu (or both) from the "Addons" menu of the sim, the only possible reasons are either the antivirus blocking the update, or a problem with your VC++ libraries, which might be missing/corrupted, even by something not related to flight sim.

Disabling the antivirus while installing its NOT enough. In addition to that, when the antivirus is suspected to be the cause of the problem (it's the more common one), you MUST also configure it to exclude the Addon Manager folder before starting the sim.

About missing/corrupted VC++ libraries. They are the 2005 SP1, the 2013 and the 2015 version. Our software doesn't require all of them but, indirectly, Simconnect itself requires it so, if one of them it's missing, you'll have lots of issues, and not just with our software.

The linked thread named "Addon Manager not showing up in P3Dv4 **SOLVED**, was quite exhaustive: